CA2753944C

CA2753944C - Method and chemical composition to improve efficiency of mechanical pulp

Info

Publication number: CA2753944C
Application number: CA2753944A
Authority: CA
Inventors: Prasad Duggirala; Sergey M. Shevchenko
Original assignee: Nalco Co LLC
Current assignee: ChampionX LLC
Priority date: 2009-03-09
Filing date: 2010-03-04
Publication date: 2018-10-02
Anticipated expiration: 2030-03-04
Also published as: BRPI1009542B1; EP2406425A1; JP5669762B2; RU2530386C2; WO2010104725A1; CA2753944A1; JP2012519785A; BRPI1009542A2; EP2406425B1; CN102348848A; KR20110128915A; RU2011135609A; KR101718557B1; US20100224333A1

Abstract

The invention provides a composition of matter and a method, which enhance the process of mechanically pulping paper precursors. The composition of matter includes a small quantity of a reducing agent and a source of alkali. When added to the pulped material, e.g., wood chips, before or during mechanical pulping, the composition reduces the energy cost of the operation.
In addition, not only does the composition also does not reduce the brightness of pulp, the composition can also enhance the effectiveness of subsequent bleaching processes.

Description

METHOD AND CHEMICAL COMPOSITION TO IMPROVE EFFICIENCY OF
MECHANICAL PULP
Cross-Reference to Related Applications None.
Statement Regarding Federally Sponsored Research or Development Not Applicable.
Background of the Invention This invention relates to improving fiber quality and process efficiency in to mechanical pulping. More specifically, the invention relates to using specialty chemical compositions such as combinations of a reductive chemical and a chelant in an alkaline medium to improve the process efficiency and brightness of a paper product produced from a pulp material manufactured in such a process. The invention has particular relevance for decreasing freeness, providing energy and chemical savings, and enhancing brightness of paper products.
Mechanical pulping is a common method to produce pulp. One advantage mechanical pulping has over other pulping methods is that the pulping process does not result in a significant loss of mass. Mechanical pulping operations unfortunately are very energy-intensive and they tend to produce pulps with low strength. Chemical treatment, such as alkalization, is sometimes used to increase strength and save energy, at the expense of brightness. Several technologies are currently practiced in mechanical pulping to manufacture products such as stone ground wood (SGW), pressurized ground wood (PGW), refiner mechanical pulp (RMP), pressurized RMP (PRMP), thermo-RMP (TRMP), and thermo-mechanical pulp (TMP).
One currently known method of reducing the energy required in mechanical pulping is through alkalization that leads to reducing the freeness of the pulp. The common prior art method of reducing the freeness of pulp is to add alkali to wood chips during the mechanical pulping process. Unfortunately, adding alkali to wood chips also causes a drop in the brightness of the resulting paper. To compensate for this brightness drop, additional bleach must be added during the bleaching stage of the papermaking process thereby reducing or eliminating any overall cost savings.
As a result, papermakers are forced to make an undesirable tradeoff. They must either choose to reduce energy costs but accept a loss in brightness or they must use additional bleach and sacrifice cost savings. Thus there is a clear need for a technology that provides energy savings without jeopardizing optical properties of paper made from such pulp.
Brief Summary of the Invention At least one embodiment of the invention is directed towards a composition and a method of its use. The composition improves the papermaking process. The composition comprises a base, a small quantity of a strong reductive chemical, and a chelating agent. The composition is added to the papermaking process before or during the mechanical pulping of wood chips. The composition decreases the energy consumption in pulp manufacturing but does not induce a net decrease in brightness of paper produced from the paper pulp when compared to paper similarly produced from similar paper pulp that did not have the composition added to its wood chips. The composition can be an aqueous solution or slurry capable of being applied at any stage of the mechanical pulping process, before or during the refining, e.g., in a wood chip washing operation, chip soaking, sprayed over the chips, and may be capable of being added directly into a refiner.
At least one embodiment of the invention is directed towards a composition wherein the base is selected from the list consisting of: an alkali or alkaline earth metal hydroxide such as sodium hydroxide, magnesium hydroxide and any combination thereof. One preferred composition can induce the resulting pulp to be more effectively bleached by peroxide or

2 hydrosulfite bleaching including but not limited to treatment with magnesium hydroxide.
Treatment of wood chips before or during mechanical pulping with small quantities of magnesium hydroxide, activates the pulp to subsequent bleaching, specifically peroxide bleaching.
At least one embodiment of the invention is directed towards a composition in which the reductive chemical is selected from the list consisting of: water soluble hydrosulfites (dithionites), sulfites, bisulfites, metabisulfites, formidinesulfinic acid, salts of formidinesulfinic acid, borohydrides, phosphines, phosphonium tertiary salts;
more specifically, alkali or alkaline earth metal hydrosulfites, borohydrides, sodium hydrosulfite, sodium borohydride and any combination thereof. The chelating agent can be a transitional metal ion chelant selected from the list consisting of: organic hydroxyacids, aminophosphonates, aminophosphates, aminocarboxylates; more specifically, salts of DTPA, salts of EDTA, salts of DTMPA, and any combination thereof.
In a specific aspect, the present invention relates to a method of improving a mechanical pulping process, the method comprising: adding a composition comprising sodium borohydride, sodium hydroxide, a chelant, magnesium hydroxide, and a reductive chemical selected from the group consisting of a hydrosulfite, a dithionite, a sulfite, a bisulfite, a metabisulfite, formidinesulfinic acid, a salt of formidinesulfinic acid, a borohydride, a phosphine, a tertiary phosphonium salt, an alkali, an alkaline earth metal hydrosulfite, sodium hydrosulfite, sodium borohydride, and any combination thereof to a pulp material prior to the conclusion of a mechanical pulping process, wherein the magnesium hydroxide is in a dosage of 0.05-0.5 wt%; bleaching the pulp material after adding the composition.
Detailed Description of the Invention The following definitions are provided to determine how terms used in this application, and in particular how the claims, are to be construed. The organization of the definitions is for convenience only and is not intended to limit any of the definitions to any particular category.

3 "CSF" means Canadian Standard Freeness a described by TAPPI methods and standards and measured in millimeters.
"Freeness" means the measure of the rate at which a suspension of pulp may be drained, and is typically measured according to the Canadian Standard Freeness test, as defined by TAPPI methods and standards. Changes in freeness can result from both chemical and physical changes in pulp.
3a "Mechanical pulping" means a physical change caused by converting pulpwood logs and chips into pulp by the use of mechanical energy.
"Chemimechanical pulping" means a mild chemical change occurring in a wood grinding or chip refining process. Chemimechanical pulping commonly improves paper strength or facilitates paper production.
"Refiner groundwood" means mechanical pulp made with a grinder and put through a rubbing, brushing, crushing, fraying, or cutting treatment in a pulp mill processing machine called a refiner.
"Refiner mechanical pulp" means pulp made by processing untreated wood chips in mechanical atmospheric refiners.
"Refiner" means a machine for mechanical treating fibers in pulp and paper mils when rubbing, brushing, crushing, fraying, or cutting is desired to process or impart certain properties to the finished pulp slurry and the sheet web formed on the paper machine.
"Small Quantity" means a concentration of an additive added to a suspension of paper pulp, which is insufficient to induce any substantial chemical changes in the pulp that are normally associated with chemimechanical pulping.
It has been known that causing a change in freeness, normally caused by alkalization, can reduce the energy needed in the pulping process (see for example US Published Application 2008/0105392). In at least one embodiment, very small quantities of chemicals are added to wood chips that results in low energy costs when the wood chips are mechanically pulped. The low energy costs are the result of a synergistic combination of the chemicals that both reduces pulp freeness and improves brightness of the pulp. Normally, freeness reduction results from the changes in physical pulp properties such as swelling of fibers. Alkaline environments can cause such swelling. However because alkali environments also increase

4

5 PCT/US2010/026148 coddation and cause phenolic group ionization in lignin, which is always present in a high-yield (mechanical) pulp, it causes yellowing of the resulting paper. As a result either the paper has a lower brightness or more bleaching chemicals must be used, thereby increasing costs.
In the Invention, this problem is addressed in two ways. First, magnesium hydroxide is used as a source of alkalinity. The magnesium hydroxide activates the pulp in the following peroxide or hydrosulfite bleaching stages, thereby increasing the degree of brightness that results from bleaching. Second, the reaction in the refiner is adjusted to be reductive not oxidative. This also inhibits any brightness loss that uncontrolled oxidation would otherwise cause. In addition, a chelating agent may be added which further reduces any yellowing because to it immobilizes transition metal cations that could otherwise catalyze yellowing reactions. In at least onc embodiment, magnesium hydroxide is combined with one or more reducing agents and, optionally, one or more chelating agents prior to the refining or in the refiner. In at least one embodiment, this combination is followed by peroxide bleaching.
In this application the specialty chemicals are used in very small quantities and are believed to operate against the pulp only at a mechanical level and not at a chemimechanical level. Because of the low quantity used, no significant chemical changes occur in the pulp. The low quantity of specialty chemicals, however, is sufficient to cause the freeness reduction in the pulp and thereby reduce the energy consumption during the mechanical pulping process. Because relatively little chemical changes occur in the pulp, this method can freely be used with most if not all currently known techniques used in most operating mills manufacturing mechanical pulp, which include but are not limited to TMP, RMP, and/or groundwood based pulps.
In at least one embodiment, small quantities of at least one reductive chemical and at least one chelant in an alkaline medium are used to treat wood chips during manufacturing of mechanical pulp. When these chemicals are so combined, instead of the brightness loss that is typical of alkaline treatments, a brightness gain occurs.
In at least one embodiment, the small quantity of at least one reductive chemical and at least one chelant in an alkaline medium, applied prior to or at the refining stage, enhances the bleaching process performed later in the paperrnaking process. In at least one embodiment, the specialty chemicals added prior to or at the refining stage (e.g., magnesium hydroxide alone or in a mixture with reductive chemical(s) and, optionally, chelant(s)) induce pulp activation towards subsequent bleaching, which then requires less bleaching materials to achieve the same degree of brightness. In at least one embodiment, the bleaching is peroxide or hydrosulfite bleaching.
to In at least one embodiment, at least one of the sources of alkali is magnesium hydroxide (MID. In at least one embodiment, the MH is used by itself, and the positive effect on brightness is observed after the peroxide or hydrosulfite bleaching stage. In at least one embodiment, the MH is combined with sodium hydrosulfite and a chelant.
In at least one embodiment, at least one of the reductive chemicals is sodium hydrosulfite (SH). In at least one embodiment, the SH is combined with magnesium hydroxide and a chelant. In at least one embodiment, small quantities of a strong reductive chemical such as SH with or without sodium borohydride (BH) are combined with MH. In at least one embodiment, small quantities of a strong reductive chemical such as SR with or without BH are combined with sodium hydroxide.
In at least one embodiment, at least one of the reductive chemicals is very small quantity of BH. In at least one embodiment, the BH is combined with sodium hydrosulfite and a chelant. In at least one embodiment the source of alkali is MH. In at least one embodiment, a small quantity of a strong reductive chemical such as SH with or without BH
are combined with MH.

6 This method makes use of chemicals commonly available in paper mills but uses them in a novel manner. As shown in the following references, while use of BH
and hydrosulfite is known in paper manufacture, it has only been used in bleaching processes, under neutral to slightly acidic conditions, and in kraft pulping processes, and not in mechanical pulping processes. (See for example patents and patent applications: US 5,129,987, EP
141826, US
2004/0000380, EP 485074,WO 88010334, EP 00027369, DE 2826821, JP 48038328 as well as journal articles: "Premix": a novel process for improving bleaching of tnechartical pulps for using a mixture of reductive agents, Wasshausen, J. et al. PuIp & Paper Canada, (2006), Volume 107 Issue 3, Pages 44-47 and New hydrosulfite route reduces groundwood bleach costs, Sellers, F. G. Pulp & Paper (1973) Volume 47 Issue 12, pages 80-82.
In addition, sodium borohydride assisted peroxide bleaching is disclosed in Further Understanding of Sodium Borohydricle Assisted Peroxide Bleaching of Mechanical Pulps, He, Th., Appita Journal (2005), Volume 58 issue 1, pages 72-76. The direct use of BH as a bleaching chemical is disclosed in US 2004/000380 WO 1996/020308, and WO
90011403 and its use as a pre-bleaching/mulit-stage bleaching chemical is disclosed in WO
01059205. Use of large amounts (1-3%) of BH on kraft pulping was described in Determination of kraft NaBH4 pulping condition of Uldag fir, by .Akgul, M., Pakistan Journal of Biological Sciences (2006) Volume 9 page 13. Finally, pre-treatment of wood chips with several chemicals for kraft and sulfite cooking is described in DE 1955641 and DE 2105324.
The use of magnesium hydroxide in the refiner is described among other places in Chinese Patent Application CN 2008-10014053 20080123. This description is directed to a process known as refiner bleaching conducted with Mg(OH)2 and hydrogen peroxide. None of any of these references describes using magnesium hydroxide in mechanical pulping, either by itself or in combination with small amounts of reductive chemicals, or use of these chemicals in

7 mechanical pulping operations in a basic envirorunent.
US 4,324,612 discusses the use of sodium dithionite which is added to a spray shower applied to a stone surface in preparation of bleached stone groundwood spruce pulp, which is then followed by further bleaching of the screened pulp in a peroxide tower. This reference however does not include the use of base for energy savings and does not mention using magnesium.
US 5,129,987 discusses refiner bleaching with alkaline sodium hydrosulfite.
This reference however is essentially a high-consistency bleaching process involving high doses of the hydrosuIfite typical of bleaching procedures.
WO 9722749 discusses a method of reducing the energy in a pulping process but it involves adjusting the pH and overall different treatment procedure targeting thc crystalline structure of cellulose..
US 5,338,402 utilizes similar chemicals to the invention but only in quantities large enough for cheminaechanical pulping, targeting different pulp properties, and underdifferent process conditions. For example, it mentions manufacturing CTMP that involves cooking at a temperature equal to or greater than 100 C using a reducing agent more electronegative than the sulfite ion together with sodium sulfite or bisulfitc or a mixture of sulfur dioxide and sodium =hydroxide. The reducing agent may be thiourea dioxide, sodium borohydride, or sodium dithionite.
Another prior art source describes a multistage pretreatment process involving a reducing agent but is dissimilar to the inventive one step process. The source describes = producing bleached pulp from wood chips via a process involving pretreatment of the chips first with at least one reducing agent (e.g., with a mixture of sodium sulfite and sodium borohydride) and then with an alkaline peroxide solution. The pretreatments were followed by refiner

8 defibration. (Brightening of Douglass-Fir Groundwood , Betz, R. G, Styan G.
E., Pulp Paper Magazine Canada (1974) Volume 75 Pages 111-114).
In another prior art, the energy expended in the mechanical refining and beating of groundwood pulps was proposed to be lowered while improving brightness and strength properties by the addition of sodium dithionite directly to the refiner or beater. (Treatment of Mechanical Wood Pulp with Reductive Bleaching Chemicals in Refiners, Melzer, J.; Auhom, W., Wochenblatt fur Papierfabrikation (1986), Volume 114, Number 8, pages 257-260_ This method however is dissimilar to the inventive process because it lacks alkali, uses much more hydrosulfite and essentially is a hydrosulfite refiner bleaching.
In at least one embodiment although the specialty chemicals darken the pulp, the resulting paper is not dark. The pulp is darkened due to alkalization.
However, because the specialty chemicals activate the pulp, the process of subsequently bleaching the darkened mechanical pulp is enhanced and less bleach is needed. This method is particularly effective with magnesium hydroxide as the source of alkali, and when the bleaching is accomplished by peroxide bleaching. Pulp activation targeted towards post-refiner bleaching can be achieved by application of magnesium hydroxide alone.
In at least one embodiment, prior to the mechanical pulp undergoing peroxide bleaching or hydrosulfite bleaching, magnesium hydroxide and sodium hydrosulfite are combined with the mechanical pulp in a refiner to produce brighter mechanical pulp. In at least one embodiment, a chelant is also added to wood chips prior to the refining operation or in the refiner.
In at least one embodiment, the specialty chemical is magnesium hydroxide, optionally with a chelant. We found that, unlike sodium hydroxide, magnesium hydroxide improves pulp brightness after hydrosulfite and, especially, peroxide bleaching by pulp activation

9 towards these processes, while immediate post-refining brightness may still decrease.
In at least one embodiment, the specialty chemicals are in the form of an aqueous solution or slurry that can be fed directly to the refiner or sprayed over wood chips.
In at least one embodiment, the specialty chemicals are in the form of an aqueous solution or slurry that can be applied on wood chips during soaking or washing operations.
The foregoing may be better understood by reference to the following example, which is presented for purposes of illustration and is not intended to limit the scope of the invention.
Several methods presented below, were used to simulate the environment 1.0 in which the invention can be practiced. Pulp samples were obtained from Midwestern American mills and from European mills (softwood TMP, TMP 1st and 2nd rejects). The doses are based on actives unless stated otherwise. DTPA has always been used in a form of a 3 8% solution (normally used in the industry) and the doses refer to this solution.
Test A. High temperature shock conditions: borohydride-based compositions with sodium hydroxide Experimental tests were conducted under wet temperature shock conditions simulating those in a refiner where to mechanical treatment occurs.
Samples of TMP were placed in stainless steel digesters and the chemicals added in water so that the end consistency was 3-5% dry pulp in slum/. The samples were kept at 150 C for

10 minutes in a rotating digester setup, cooled down, washed, pH measured and had handsheets made from them. The pH in all the samples went from alkaline to slightly acidic, indicating a finished chemical reaction; therefore no acidification of the slurries was needed.

Test B. Moderate temperature shock conditions: hydrosulfite-containing compositions with sodium hydroxide Experimental tests were conducted under wet temperature shock conditions simulating those in a refiner where mechanical treatment occurs.
Samples of TMP were placed in degassed flasks under septa (soft plastic that protects the content from air but can be penetrated with a needle) and chemicals were added via a syringe in a flow of nitrogen, to a total consistency of 3.6%. The samples were kept at 80 C for 1 hour minutes in a water bath, cooled down, washed, pH measured and handsheets were 10 made upon acidification to pH 5. The pH of the samples after the process was slightly alkaline. In a test where sodium borohydride was applied, it was used in a form of Rolim&Haas' product Borol, which is (39% NaOH, 12% NaBH4). The target alkalinity (for example, 0.75% NaOH, 0.25% NaBH4 to o.d. pulp) was maintained by varying quantities of introduced sodium hydroxide.
Test C. Hydrosulfite treatment with sodium hydroxide followed by bleaching The samples were prepared as described in Test B, washed, dewatered and bleached under standard conditions (70 C, 1 h, 1.5% Na0II, 2% H202). The samples were washed, and handsheets were made upon acidification to pH 5.
Test D. Freeness improvement A protocol was developed that simulated both mechanical and temperature effects of the thennomechanical process better that just a shock temperature treatment.

11 The pulp was mixed with the chemicals at 10% consistency and then beaten in a PFI-type laboratory pulp refiner (150 C). Then the pulp was diluted to 3% and exposed to heat as described in Test A. Freeness (CSF) of the pulp treated in presence of 035-1%
NaOH
was about 20 ml lower than in the control; borohydride and DTPA did not affect the result.
Test E. High temperature shock conditions: hydrosulfite-containing compositions with magnesium hydroxide A brightness test was conducted under wet temperature shock conditions simulating those in the refiner (no mechanical treatment). Samples of TMP were placed in plastic bags and mixed well with magnesium hydroxide and DTPA. The bags were opened, and the samples transferred into stainless steel digesters and degassed with nitrogen, for 7 minutes each. The remaining chemicals were added via a syringe into the volume of the pulp in a nitrogen flow. The 5%-consistency samples were kept at for 10 min in a rotating digester setup, cooled down, washed, pH measured and either handsheets were made or the pulp was subsequently bleached. The pH in all of the samples went from alkaline to slightly acidic, indicating a finished chemical reaction;
therefore no acidification of the slurries was needed.
Test F. Moderate temperature shock conditions: hydrosulfite-containing compositions with magnesium hydroxide The assessment of the effect of reductive chemicals on brightness was conducted under wet temperature shock conditions simulating those in the refiner (no mechanical treatment). Samples of TMP were placed in degassed flasks under septa and

12 chemicals added via a syringe, to total consistency 5%. Magnesium hydroxide as a dilute slurry and DTPA were added first, mixed well with the pulp, then reductive chemicals added. After mixing, the samples were kept at 80 C for 1 h 15 min in a water bath, cooled down, washed, and pH measured and handsheet made (no pH adjustment) or the pulp subsequently bleached.
Test G. Hydrosulfite treatment with magnesium hydroxide followed by peroxide bleaching Samples were prepared as described in Test E or F, washed with 2L DI
water, dewatered and bleached under standard conditions (70 C, 1 h, 1.5% NaOH, 2%
H202). The samples were washed with 2L DI water and handsheets made upon acidification to pH 5.
Test H. Hydrosulfite treatment with magnesium hydroxide followed by hydrosulfite bleaching = Samples were prepared as described in Test E or F, washed with 1L DI
water, dewatered and bleached under standard conditions (70 C, 1 h, 1 Na2S204). The samples were washed with 2L DI water, and handsheets were made.
The results of tests A-H are provided in the following tables 1-18 in which the parenthesis next to the table number indicates which data corresponds to which tests.

13 TABLES
Table 1 (A) Sample Brightness Control 52.10 0.5% NaOH 49.66 0.5% NaOH + 0.25% NaBH4 52.96 0.5% NaOH + 0.1% NaBila 51.71 Table 2 (A) Sample Brightness Control 52.82 0.5% NaOH 49.64 0.5% NaOH + 0.1% NaBH4 51.88 0.5% NaOH + 0.1% NaBH4 + 0.1% DTPA 52.53 1% (CH3)4NOH 50.38 1% (CH3)4NOH + 0.1% NaBH4 51.95 0.5% NaOH + 0.25% RHOCH2)4P12SO4 51.44 The data of Tables 1 and 2 demonstrate that minimal quantities of the specialty chemicals can fully compensate for the brightness loss due to alkalization of the pulp. A chelant noticeably increases the effect of borohydrate.

14 Table 3 (A) Sample Brightness Control 52.42 0.75% NaOH 50.02 0.75% NaOH + 0.25% NaBH4 52.88 0.75% NaOH + 0.1% NaBH4 52.10 0.75% NaOH + 0.1% NaBH4 + 0.1% DTPA 53.13 1% NaOH + 0.25% NaBH4 5L92 Table 4 (A) Sample Brightness Control 52.30 0.75% NaOH 49.27 0.75% NaOH + 0.23% NaBH4 52.5 0.75% NaOH + 0.1% NaBH4 51.62 0.75% NaOH + 0.05% NaBH4 51.01 0.75% NaOH + 0.05% NaBH4 + 0.05% DTPA 51.47 0.75% NaOH + 0.025% NaBH4 + 0.05% DTPA 50.6 The data in Table 3 and 4 demonstrate that the optimal alkalinity that can be applied without a brightness loss is 0.75%.

Table 5 (B) Sample Brightness Control 55.82 0.75% NaOH ' 54.08 0.75% NaOH + 0.2% Na2S204 55.02 0.75% NaOH + 0.5% Na2S204 55.92 0.75% NaOH + 0.2% Na2S204 + 0.05% NaBH4 55.98 0.75% NaOH + 0.2% Na2S204 + 0.05% NaBH4 + 0.05% DTPA 56.21 0.75% NaOH 0.2% Na2S204 + 0.025% NaBH4 + 0.05% DTPA 55.66 Table 5 lists the effect on brightness upon the thermal treatment of the pulp after the composition underwent peroxide bleaching.
Tables 6-9 list the effect of the compositions (prototype products, 27% total solids) on paper products.
Table 6 (C) Sample Brightness Control 61.17 0.75% NaOH 59.78 0.75% NaOH + 0.3% Na2S204 + 0.05% DTPA 62.33 0.75% NaOH + 0.3% Na2S204 + 0.025% NaBH4 + 0.05% DTPA (I) 63.79 0.75% NaOH + 0.3% Na2S204 + 0.0125% NaBH4 + 0.05% DTPA (II) 63.81 Table 7 (C) Sample Brightness Control 61.36 0.75% NaOH 58.90 0.75% NaOH + 0.025% NaB114 + 0.05% DTPA 63.46 0.75% NaOH + 0.3% Na2S204 0.025% NaBH4 + 0.05% DTPA (I) 66.38 0.75% NaOH + 0.3% Na2S204 + 0.0125% NaBH4 + 0.05% DTPA 64.22 Table 8 (C) Sample Brightness Control 60.34 0.75% NaOH 58.57 0.75% NaOH + 0.3% Na2S204 0.025% NaBH4 + 0.05% DTPA 65.48 0.75% NaOH + 0.3% Na25204 + 0.0125% NaBH4 + 0.05% DTPA 65.74 Tables 9 and 10 provide the effect of one of preferred compositions, 19% NaOH, 0.316% NaBH4, 0.48% DTPA, 6.32% Na2S204 (26.1-27.2% solids, depends on the impurities in the solid hydrosulfite). The composition was then diluted in paper pulp slurry so that the NaOH
was reduced to 0.75% to o.d. pulp.

Table 9 (B) Sample Brightness Control 49.71 0.75% NaOH 48.62 Prototype Product (first try) 50.57 Prototype Product (second try) 49.83 Prototype Product (third try) 50.01 Table 10 (B) Sample Brightness Control 49.40 0.75% NaOH 46.68 Prototype Product (first try) 49.45 Prototype Product (second try) 50.15 Prototype Product (third try) 50.06 Table 11 indicates the effect of using magnesium hydroxide as the alkali.
Magnesium hydroxide is less expensive than other alkali. Compositions containing magnesium hydroxide requires less energy to undergo the pulping process. When substituting magnesium hydroxide for sodium hydroxide the replacement ratio is 0.75% sodium hydroxide for 0.5%
magnesium hydroxide.
Table 11 (F,G) Brightness, Brightness, unbleached bleached Control 49.09 55.18 0.5% Mg(OH)2 49.05 60.49 0.5% Mg(OH)2+0.05%DTPA 49.67 60.86 0.5% Mg(OH)2+0.05%DTPA 52.28 61.99 +0.25% Na2S204 0.5% Mg(OH)2+0.05%DTPA 54.44 62.42 +0.25% Na2S204+0.0125%NaBH4 0.25% Mg(OH)2+0.05%DTPA 53.56 62.54 +0.125% Na2S204+0.0125%NaBH4 0.25% Mg(OH)2 49.91 61.15 0.05%DTPA 50.45 56.58 Table 12 (F, G) Brightness, bleached Control 55.41 0.5% Mg(OH)2+0.05%DTPA 62.11 +0.25% Na2S204 0.5% Mg(OH)2+0.05%DTPA 61.07 +0.125% Na2S204 0.5% Mg(OH)2+0.05%DTPA 61.34 +0.125%Na2S204+0.0125%NaBH4 0.125% Mg(OH)2+0.05%DTPA 61.90 +0.125% Na2S204 0.125% Mg(OH)2+0.05%DTPA 62.03 +0.125%Na2S204+0.0125%NaBH4 0.125% Mg(OH)2 61.17 Table 13 (E,G) Brightness, Brightness, unbleached bleached Control 49.67 54.17 0.5% Mg(OH)2 46.92 57.72 0.5% Mg(OH)2+0.05%DTPA 46.50 59.35 0.5% Mg(OH)2+0.05%DTPA+0.25% Na2S204 49.68 59.85 0.5%Mg(OH)2+0.05%DTPA+0.25% 50.27 60.05 Na2S204+0.0125%NaBH4=
0.25% Mg(OH)2+0.05%DTPA+0.125% 52.76 61.48 Na2S204+0.0125%NaBH4 0.25% Mg(OH)2 48.03 59.17 0.05%DTPA 49.46 56.21 Table 14 (E,G) Brightness, Brightness, unbleached bleached Control 48.58 54.4 0.5% Mg(OH)2 46.95 58.95 0.75% NaOH 47.59 48.55 0.5% Mg(OH)2+0.05%DTPA 51.55 60.74 +0.25% Na2S204+0.0125%NaBH4 0.25% Mg(OH)2+0.05%DTPA 54.33 61.77 +0.25% Na2S204+0.0125%NaBH4 Prototype Product based on NaOH, 50.41 53 .17 see above (0.75% NaOH) Prototype Product based on NaOH, 50.59 53.36 see above (0.75% NaOH) Control, bleaching with 0.05% MgSO4 54.61 Control, bleaching with 0.05% MgSO4 55.42 + 0.05%DTPA*
The data from Tables 11-14 demonstrate why using magnesium hydroxide is preferred. There is no magnesium-related brightness loss under moderate conditions (75 C, no bleaching), while under severe conditions (150 C, no bleaching) better simulating a refining process, magnesium-related brightness loss occurs. However, in both cases there is a significant magnesium-induced brightness improvement after bleaching. Reductive chemicals further significantly improve post-refining brightness: a major effect of hydrosulfite, less from extra borohydride. Magnesium-reductive pulp pre-treatment clearly shows performance in refining applications. This effect is new and, as shown in Tables 14-16 (alternative pulps were used in 15 and 16), it cannot be achieved by just presence of magnesium ions in the pulping slurry. The pre-treatment is required, and this stage is automatically achieved when the proposed chemistry is present at the stage of mechanical pulping.

Table 15 (G) Chemistry Application Brightness Control 56.40 0.05%
MgSO4-1-0.125%DTPA In liquor 57.47 0.125% MgSO4 Mixed with pulp before bleaching 57.95 0.25% MgSO4 Mixed with pulp before bleaching 58.17 0.125% Mg(OH)2 Mixed with pulp before bleaching 58.60 0.25% Mg(OH)2 Mixed with pulp before bleaching 58.84 Mixed with pulp, kept at 50 C
0.125% Mg(OH)2 for 30 min before bleaching 60.18 Mixed with pulp, kept at 50 C
0.25% Mg(OH)2 for 30 min before bleaching 60.36 Mixed with pulp, kept at 70 C
0.125% Mg(OH)2 for 60 min before bleaching 60.23 Mixed with pulp, kept at 70 C
0.25% Mg(OH)2 for 60 min before bleaching 60.07 10 Table 16 (F,G) Brightness, bleached Control 59.50 0.5% Mg(OH)2+0.05%DTPA 66.93 +0.25% Na2S204 0.5% Mg(OH)2+0.05%DTPA 66.12 +0.125% Na2S204 0.125% Mg(OH)2+0.05%DTPA 66.42 +0.125% Na2S204 0.125% Mg(OH)2+0.05%DTPA 67.14 +0.125%Na2S204+0.0125%NaBH4 The positive effect of the specialty chemicals is also observed in the subsequent hydrosulfite bleaching as illustrated in Tables 17 (mild conditions, full compensation) and 18 (severe conditions better simulating the refining process, a significant brightness gain).

Table 17 (F,H) Sample Brightness Control 59.22 0.5% Mg(011)2 57.79 0.5% Mg(OH)2+0.05%DTPA
+0.25%Na2S204+0.0125%NaBH4 59.68 0.5% Mg(OH)2+0.05%DTPA
+0.125% Na2S204 58.43 Table 18 (E,H) Sample Brightness Control 51.42 0.5% Mg(OH)2 51.97 0.5% Mg(OH)2+0.05%DTPA 52.46 0.5% Mg(OH)2+0.05%DTPA
+0:25% Na2S204 56.03 0.5% Mg(OH)2+0.05%DTPA
+0.25%Na2S204+0.0125%NaBH4 55.43 0.5% Mg(OH)2+0.05%DTPA
+0.125%Na2S204+0.0125%NaBH4 53.67 Changes can be made in the composition, operation, and arrangement of the method of the invention described herein without departing from the concept and scope of the invention as defined in the claims. While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. Furthermore, the invention encompasses any possible combination of some or all of the various embodiments described herein. All patents, patent applications, and other cited materials mentioned anywhere in this application or in any cited patent, cited patent application, or other cited material are hereby incorporated by reference in their entirety.

The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term "comprising" means "including, but not limited to". Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.
This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.

Claims

CLAIMS:

1. A method of improving a mechanical pulping process, the method comprising:
adding a composition comprising sodium borohydride, sodium hydroxide, a chelant, magnesium hydroxide, and a reductive chemical selected from the group consisting of a hydrosulfite, a dithionite, a sulfite, a bisulfite, a metabisulfite, formidinesulfinic acid, a salt of formidinesulfinic acid, a borohydride, a phosphine, a tertiary phosphonium salt, an alkali, an alkaline earth metal hydrosulfite, sodium hydrosulfite, sodium borohydride, and any combination thereof to a pulp material prior to the conclusion of a mechanical pulping process, wherein the magnesium hydroxide is in a dosage of 0.05-0.5 wt%;
bleaching the pulp material after adding the composition.

2. The method of claim 1, wherein the composition is an aqueous solution or slurry which is added: (i) by spraying over a wood chip, soaking a wood chip or washing a wood chip, (ii) in a refiner, or (iii) a combination of (i) and (ii).

3. The method of claim 1, further comprising the step of combining magnesium hydroxide with sodium hydrosulfite in a refiner.

4. The method of claim 1, wherein the chelant is a transitional metal ion chelant selected from the group consisting of: organic hydroxyacids, aminophosphonates, aminophosphates, aminocarboxylates, salts of DTPA, salts of EDTA, salts of DTMPA, and any combination thereof.

5. The method of claim 1, wherein the composition comprises 5- 20 wt%
sodium borohydride.